1. Field of the Invention
The present invention relates to a spindle motor for information equipment and audio and visual equipment, and more particularly to a spindle motor which excels in durability and reliability and is optimally suited to a laser printer, a scanner motor for a digital copying machine, a magnetic hard disk drive (hereafter abbreviated as the HDD), an optical disk drive, and the like.
2. Description of the Related Art
As a conventional spindle motor of this type, a spindle motor for a HDD, such as the one shown in FIG. 11, is known. In this spindle motor, a sleeve 2 is secured to a base 1, a shaft 3 is rotatably inserted in the sleeve 2, and a hub 4 is integrally attached to this shaft 3.
A lower end face of the shaft 3 is formed as a thrust receiving surface 3s, a thrust plate 6 having a thrust bearing surface 6s opposing this thrust receiving surface 3s is secured to the base 1, and a dynamic-pressure generating groove 7 of, for example, a spiral shape is provided in at least one of the thrust receiving surface 3s and the thrust bearing surface 6s, thereby forming a thrust fluid bearing S.
Meanwhile, a pair of radial receiving surfaces 3r are formed on an outer peripheral surface of the shaft 3 at upper and lower positions with an axial interval therebetween, while a pair of radial bearing surfaces 2r opposing the radial receiving surfaces 3r are formed on an inner peripheral surface of the sleeve 2, and a pair of dynamic-pressure generating grooves 8 of, for example, a herringbone-shape are provided in at least one of the radial receiving surfaces 3r and the radial bearing surfaces 2r, thereby forming a radial fluid bearing R.
The shaft 3 and the hub 4 are integrally driven rotatively by a motor M comprised of a stator 9 fixed to an outer periphery of the base 1 and a rotor magnet 10 fixed to an inside-diameter surface of the hub 4.
When the shaft 3 rotates, dynamic pressure is generated in a lubricant in each bearing clearance by means of the pumping action of the respective dynamic-pressure generating grooves 7 and 8 of the thrust fluid bearing S and the radial fluid bearing R, so that the shaft 3 is supported in a state of noncontact with the sleeve 2 and the thrust plate 6.
However, with the spindle motor in which the thrust fluid bearing S and the radial fluid bearing R are thus adopted as its bearings, if the spindle motor is used over extended periods of time, the lubricant held in the bearing clearances gradually decreases due to its evaporation and scattering during rotation. As a result, lubrication becomes faulty, so that if an attempt is made to use the spindle motor beyond the service life of the bearings, there has been the risk that the bearings become seized.
In addition, at the time of assembling by inserting the shaft 3 into the sleeve 2, the shaft 3 is inserted after a predetermined amount of lubricant is poured in advance onto a closed cylindrical surface in the space surrounded by the inner peripheral surface of the sleeve 2 and the thrust plate 6. For this reason, there has been a problem in that air is liable to become contained, and slight bubbles are liable to remain in the bearing clearances. The remaining bubbles can possibly cause the lubricant in the bearing clearances to be extruded to the outside as the bubbles expand due to a change in the atmospheric pressure which can occur when the assembled spindle motor product is transported by such as an airplane or due to a temperature rise during the rotation of the spindle motor in use.